The present invention relates, in general, to magnetic tape data storage devices and, more particularly, to tracking the remaining useful life of a magnetic data storage tape.
Magnetic tape data storage devices, or xe2x80x9ctape drives,xe2x80x9d have long been key devices in computer systems for storing digital data in nonvolatile form. In many systems, tape drives have become important secondary data storage devices for the purposes of redundant data storage (or xe2x80x9cbackupxe2x80x9d) and retrieval (or xe2x80x9crestorexe2x80x9d). Magnetic tape has been recognized by computer users as a cost-effective medium for redundantly backing up data already present on other primary nonvolatile data storage devices, such as magnetic disk drives. That stored data is then available to be restored to another primary storage device in the case that the disk drive becomes inoperative. Furthermore, in order to restore data that is relatively pertinent and up-to-date, the backup operation is usually performed frequently enough to allow restoring of data that is not significantly out-of-date compared to the data on the disk drive.
Often, a relatively small set of magnetic tape cartridges is used in rotation to backup the disk drive at sufficient intervals since data from very old backup operations is usually of little use. As a result, each of the magnetic tapes may be recorded, or xe2x80x9cwritten,xe2x80x9d many times, and the data on the tape may be retrieved, or xe2x80x9cread,xe2x80x9d as a part of the restore process, or to verify the validity of data just written to the tape.
Magnetic tapes used for backup purposes must be extremely reliable if they are to be used as insurance against a failure of the primary data storage device. However, after a tape has been used many times during backup operations, it can become increasingly difficult for the data to be retrieved without encountering permanent data errors due to the amount of wear incurred by the tape. The passing of the tape over and through various mechanical portions of the drive (such as the read-write head and tape rollers) causes the tape to wear. The degree of wear of a tape is, therefore, most directly dependent on how much the tape has been read and written. Since tapes used for data backup are often written a multitude of times and are thus susceptible to the problems associated with excessive wear, a method of determining and reporting when a tape has reached its useful life becomes valuable in helping prevent the use of a tape for data backup when the tape is worn to the point where retrieval of data may become problematic.
In some magnetic tape implementations, the amount of wear incurred by the tape is ascertained by the tape drive keeping track of the frequency and severity of read errors encountered during tape read operations. Once the frequency or severity of read errors surpasses a predetermined threshold, the user is informed in some way that the tape has exceeded its useful life, and should be replaced. Similar methods of error tracking are also used in magnetic hard disk drives and optical disk drives. Such a method requires rather extensive record-keeping and analysis on the part of the tape drive to determine if the tape has experienced sufficient wear to be replaced.
An alternative method that requires little analysis on the part of the tape drive is to compare the cumulative use of the tape to the tape manufacturer""s recommended usage specifications. For example, manufacturers of QIC (quarter-inch-cartridge) TRAVAN tape minicartridges generally specify a maximum of approximately 10,000 end-to-end tape passes for their products, where each end-to-end pass is a read or write operation that traverses the entire length of the tape. Tape drives that write to and read from TRAVAN minicartridges employ a longitudinal recording method, whereby data is written in data xe2x80x9ctracksxe2x80x9d that extend lengthwise along the tape. Thus, the reading or writing of an entire track constitutes an end-to-end pass of the tape.
One such standardized implementation of this method is integrated in a status-reporting mechanism called TAPEALERT, which is well-known in the art and has been modified for use with TRAVAN magnetic tape minicartridge drives, which are used primarily for data backup and restore of personal computers. Among other functions, such as reporting current drive operational status, TAPEALERT provides an indication of the useful life of the tape currently loaded in the drive. TRAVAN tape minicartridges employ a xe2x80x9cwrite pass countxe2x80x9d field as part of the control information found on the tape. The write pass count indicates the number of complete write operations that have been performed on the tape. Once the value in that data field reaches a certain predefined numerical limit, the tape drive in which the tape is loaded informs the computer connected to the drive that the tape has reached the end of its useful life, and must be replaced.
Due to the limitations on the types of information provided by the TRAVAN standard data format, data wear is estimated by using the number of complete write operations as reported in the control information on the tape. Unfortunately, this number does not necessarily correlate with the amount of wear the tape has endured. For example, a backup operation can easily consist of a write operation of several tracks, with each track requiring one pass of the tape over the reading mechanism. Such a use of the tape will be identified as a single write operation by TAPEALERT. In some implementations of TAPEALERT, the predefined numerical limit is set to compensate for such a possibility, assuming that a typical data backup operation utilizes, for example, about 80 percent of the tape. However, a more accurate way to more closely track the use of a tape would be advantageous.
Additionally, TAPEALERT provides a single type of warning, indicating that the tape has reached the end of its useful life, and should be replaced immediately. Ideally, it would be desirable if one or more early warnings could be given to the user, indicating that the tape was approaching, but had not necessarily exceeded, its useful life.
Accordingly, a need exists for a method that more closely monitors the amount of useful life remaining in a magnetic data storage tape and reports that useful life to the user in a more descriptive fashion.
In a possible embodiment, the invention provides the user with a timely, accurate assessment of the useful life remaining on a magnetic data storage tape. The actual usage of the tape is tracked closely in terms of end-to-end passes performed on the tape. This data is then used to inform the user when the tape is nearing or has surpassed its recommended life. Such an embodiment is easily implementable in the tape drive firmware and the software of the computer connected to the tape drive while providing valuable information concerning the remaining useful life of the tape to the user.
Briefly and in general terms, a method of tracking the useful life remaining on a magnetic data storage tape according to an example embodiment of the invention is begun by establishing the ability of the tape to store a data field indicating [that] the total number of end-to-end passes in some form. By example, this task can be implemented by the drive checking for a special identification field on the tape which indicates that the tape has been xe2x80x9cformattedxe2x80x9d for use by the invention. (xe2x80x9cFormattingxe2x80x9d is the process of writing certain control information on the tape to allow the writing and reading of user information by a tape drive.) If no valid indication exists, the method of determining the useful life of the tape cannot be utilized on that cartridge, and the user can be notified of this fact. Otherwise, the data field can be initialized with a starting value indicating that no end-to-end passes have been performed if that data field has not been previously written.
Assuming the tape is formatted and initialized for use with the proposed method, the drive is then responsible for maintaining an indication of the number of end-to-end passes on the tape to reflect the use of the tape by the drive. In an example embodiment, the form of that value can be the total number of end-to-end read and write passes, or just the number of end-to-end write passes, with a read pass assumed as a verification for each write pass. In such an embodiment, the value is maintained by adding to the value the number of write (or read and write) passes that have been performed on the tape since the value on the tape was last written, and storing that value back on the tape. The drive then passes to the computer that information, either in its original form, or in a xe2x80x9cquantizedxe2x80x9d form, whereby the information is placed in a descriptive category, such as xe2x80x9cuseful life exceeded,xe2x80x9d or xe2x80x9cnearing recommended useful life.xe2x80x9d That information, indicating the usage level status of the tape, is then transferred to the attached computer for the user.
Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. Also, the claims alone, and not the preceding summary or the following detailed description, define the present invention.